1. Field of the Invention
The present invention relates to memory circuit boards installed in computer systems.
2. Description of the Prior Art
Many computer systems utilize what are called mother boards, system boards, or main boards which contain signal busses, microprocessors, device controllers, device interface connectors, and expansion slots. The system boards generally include some amount of base memory on the board itself. The system boards may also include predesignated locations or sockets for the installation of additional semiconductor memory chips, thereby increasing the base memory of the computer system. However, factors such as system board space allocation place a practical limit on the amount of memory which may be added to a system board.
One manner of addressing this practical limitation is to add memory through the use of circuit boards external to the main system board. These external memory boards are connected to the system board by means of connectors or slots on the system board. Generally, a memory expansion board is inserted into one of the system board's expansion slots and the computer system is updated as to the total amount of available memory to include the base memory on the system board and the memory on the expansion board. The means of updating the computer system as to the total memory available may include mechanical means, such a switches or jumpers, or electronic means, such as setting certain signal lines to certain levels.
Another manner of addressing the space limitations of the system board was to use single inline memory modules (SIMM's) on the system board. On a SIMM the memory devices use very small packages and are very densely packed, so that a large amount of memory can be installed in a small area. The SIMM is installed in a connector on the system board and are installed perpendicular to the system board, thus using little space.
Recent developments in computer technology, particularly in the area of microcomputers have lead to an increase in the amount of total memory which may be effectively managed by the computer systems. With the introduction of Intel Corporation's 80386 microprocessor, microcomputers are now capable of managing in excess of 16 megabytes (Mb) of memory. With the advancement of gate array and application specific integrated circuits (ASIC's) many functions previously performed on interchangeable circuit boards located in slots on the system board have been integrated onto the system board. Thus, system board space becomes even more precious and memory areas must be very dense. The space problem on the memory board can become so severe that even the use of SIMM's can not be tolerated and all the memory must be placed on external circuit boards.
Personal computers are generally designed to use circuit boards conforming to a selected standard for expansion. One such standard is the Industry Standard Architecture (ISA) which is based on the IBM PC/AT manufactured by International Business Machines Corporation (IBM). The use of the ISA standard limits the physical size of the circuit boards and memory boards which can be installed in the computer system. This size limitation, when coupled with the addressing capabilities of the microprocessors such as the 80386 and the demands for memory developed by many computer programs currently available, limits the amount of memory which can be installed on an external circuit board. The use of SIMM's may result in sufficient memory being available or being capable of being installed on the circuit board.
However, the use of SIMMs imposes a practical limitation on the computer system. The physical height of the modules, when mounted on the external circuit board effectively renders closely adjacent expansion slots unusable. Thus, the use of SIMMs have the effect of decreasing the number of expansion slots available in the computer system, thereby decreasing the flexibility of a computer system.